EXPLANATION OF THE DIAGRAM. 67 



naturally distinct parts of tlie structure which we are 

 examining. 



But although it is desirable to keep these caveats in our 

 memory, I do not think that either the artificial nature of 

 psychological classification or the fact that we have to do 

 with a gradual process of evolution, constitutes any serious 

 vitiation of the mode of representation which I have adopted. 

 For, on the one hand, some classification of faculties we must 

 have for the purposes of our inquiry ; and, on the other hand, 

 I have as much as possible allowed for the unavoidable defect 

 in the representation which arises from evolution being 

 gradual, by making the branches of the arborescent structure 

 wide at their bases, and by allowing each of them, after giving 

 off the next succeeding branch, to continue on its own course of 

 development ; so that both the parent and daughter faculty 

 are represented as occupying for a more or less considerable 

 distance the same levels of develoj^ment — in each case my 

 estimate of the comparative elaboration which the completed 

 faculty betokens being represented by the vertical height of 

 its apex. Besides, as already stated, faculties named in the 

 two parallel columns are written upon those levels where !'■ 

 have either a j^'^^iori reasons or actual evidence to conclude > 

 that they first definitely appear in the growing structure of' 

 Mind ; in this way the difficult question of assigning the 

 lower limit of evolution at which any particular faculty 

 begins to dawn is as much as possible avoided. 



It is almost needless to add that in preparing this diagram 

 I have resorted to speculation in as small a measure as the 

 nature of the subject permits. Nevertheless it is obvious' 

 that the nature of the subject is such that, in order to com- 

 plete the diagram in some of its parts, I have been obliged to 

 resort to speculation pretty largely. I think, however, that 

 as the exposition proceeds, it will be seen that, if the funda- 

 mental hypothesis of mental evolution having taken place is 

 granted, my reasoning as to the probable history of the pro- 

 cess does not anywhere involve speculation of an extravagant 

 or dangerous kind. In matters of detail — such, for instance, 

 as the comparative elevation of the different branches in the 

 psychological tree — my estimates may, probably enough, be 

 more or less erroneous ; but the main facts as to the sequence 

 of the faculties in the order of their comparative degrees of 

 elaboration are mere corollaries from our fundamental h}^o- 



E 2 



